Then I met Peter. Peter is a very nice guy who uses a 5D, and he shoots architecture, and he has an EE-S screen, and he needs a grid screen, and...Well, long story short. We exchanged the screens.
At first, the differences weren't that great in use between the grid and the darker EE-S screen, except that it's at least a stop darker, but as I have used it a bit more, I feel pretty comfortable getting accurate focusing, fast. Probably not as accurate as a split screen, but much better than the stock screen. The only down side is, of course, the very dark screen when using slower lenses. Although the screen is easy to change, it's inconvenient to do if you change lens a lot.
As its intended use, this screen is much better when used on very fast lenses. Ideal for lenses with aperture of f2 or faster. But, I regularly stop down the lenses to f8 to f11 and the screen still works well.
My conclusion is: buy it if you work with manual focus lenses a lot. Buy it from e-Bay. It's much cheaper. The local Henry's wants $75 for a piece of plastic, which can be had for half the price.
Daisy -- 5D & Leica R 90mm f2.8 (E55).
William -- 5D & Leica R 90mm f2.8 (E55)